1. Field of the Invention
The present invention relates to mobile computers for performing communication while moving between a plurality of interconnected networks. The invention also relates to a position identifier management apparatus and method, and a position identifier processing method for processing position identifiers concerning the above-described mobile computers.
2. Description of the Related Art
Along with the widespread use of the Internet, which is the largest worldwide computer network, users have become able to obtain publicly available information and services by connecting to the Internet, and also, new computer businesses are being developed by providing information and services to users who make access through the Internet. New technologies for the use of the Internet are also being developed. Additionally, due to a progress in the implementation techniques of computers, small and light computers are becoming popular, and it is no longer unusual for the users to carry computers with them.
In the Internet, each computer possesses an identifier, which is referred to as an Internet protocol (IP) address”, and based on the IP addresses, packet switching is performed. However, IP addresses serve not only as identifiers for computers, but also as identifiers representing the positions of computers on a network (hereinafter sometimes referred to as “position identifiers”). Accordingly, when a computer is moved on a network, it is handled as different computers on the network before and after being moved, even though they are actually the same computer.
In today's world in which mobile computers have become widespread, it is inconvenient if the same computer is handled as different computers every time it is moved. For example, a system administrator is unable to conduct authentication based on IP addresses as intended, or the session used while the computer is moved is terminated.
In order to avoid such problems, the Internet Engineering Task Force (IETF), which is an IP standardizing organization, has set up a mobile IP. The mobile IP is a system in which a mobile computer is able to use the unique IP address (which is referred to as the “home address”) without depending on where the computer is positioned on a network.
A mobile computer sets this home address as the source address of an IP packet. A receiver receives the packet and then sends a packet to the mobile computer by setting the home address as the destination address. With this arrangement, however, the packet will not reach the mobile computer which has been moved away from the home address. Thus, according to the mobile IP, a home agent is provided on the network which is compatible with the home address. When a packet is sent to the mobile computer which has been moved away from the home address, the home agent receives the packet for the mobile computer and transfers it to the mobile computer. The mobile computer regularly reports the current position to the home agent.
According to the above-described control, when the mobile computer moves, communication between the mobile computer and a receiver is performed in a path, which is formed in a triangle shape, via the home agent. This is redundant and lowers the transmission efficiency. In order to solve this problem, optimization of the path has been proposed in the mobile IP. In order to optimize the path, the mobile computer reports the current position thereof to the receiver, and the receiver transfers the packet addressed to the home address to the current position of the mobile computer, thereby eliminating the redundancy of the path.
However, such a mobile IP presents the following problems.
The presence of the home agent is essential, and the home agent must be positioned on the network which is compatible with the home address. This makes it difficult to ensure redundancy of the home agent because there is only one home address, and there is only one IP network which is compatible with the home address. In other words, it is possible to provide a plurality of home agents on one network, but it is impossible to provide a home agent on another network to improve redundancy. Thus, although redundancy against a failure occurring in the home agent apparatus can be ensured, redundancy against a failure occurring in the network on which the home agent is placed cannot be ensured.
The problem of the protocol overhead is also encountered. Basically, for transmitting packets to a mobile node (computer), an encapsulating technique employed on the same layer, which is referred to as the “tunneling technique”, is employed. A header providing technique for controlling the path is also employed. In this technique, when transmitting a packet to a mobile node, not only the home address, but also routing header information is added to the header, thereby directly transmitting the packet to the mobile node without via the home agent. According to these techniques, the data amount of protocol header is increased, and the substantial communication performance is lowered.
Additionally, in the mobile IP of IP version 6 (IPv6), new options have been defined after products manufactured based on the fundamental standards of IPv6 were put on sale. Accordingly, new nodes implemented based on the new options may not be able to communicate with the old nodes implemented based on the old basic standards.
In short, according to the conventional mobile IP technique, the redundancy of the home agent for managing the relationship between the home address of a mobile computer and the current position thereof cannot be enhanced. Additionally, the protocol overhead is increased, and communication cannot be performed between nodes having basic IPv6 standards and new nodes having the mobile IP.